Blasting composition



United States Patent Ofiiice 3,129,127. Patented Apr. 14-, 1964 3,129,127 BLASTING COMPOSITKQN Cyril J. Brena, Smithsburg, Md., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., :1 corporation of Delaware No Drawing. Filed Feb. 17, 1961, Ser. No. 89,916 3 Claims. (Cl. 14930) The present invention relates to an improved blasting agent composition.

The main function of an explosive charge in blasting operations is to provide the energy required to release material from its natural formation and to render the material in a form in which it can be handled or processed with minimum difiiculty. The cost of recovering the desired material in usable form is inherently dependent on the cost of the explosive composition used and the cost of preparing the site for the blasting operation. For this reason much effort has been expended in the past to reduce the cost of the explosive composition and also to reduce the cost of preparing the side for blasting. The attainment of both goals has not always led in the same direction. For example, the cost of preparing a site for blasting can be reduced if fewer boreholes are required per ton of material released. Because the energy required to release the material remains the same, fewer boreholes are practical only if the energy per borehole can be increased and if the material to he moved will break properly with wider hole spacings. One method of accomplishing such increased energy per borehole is by drilling larger boreholes. Within limits, some economy can be effected by such procedure but the additional cost of drilling larger boreholes prevents unlimited extension of this technique.

An alternate method to reduce overall blasting costs is to use very high density, high energy exposives, which will permit increased hole spacings without increasing hole diameter and thereby represents decreased drill costs. In the past, high energy density has been attainable by using larger percentages of high explosive compounds such as nitroglycerin or high density fuels such as ferrosilicon. While these measures are eifective in producing high energy, high density explosives, high ingredient costs in many instances limit their acceptance and use by the trade.

Low cost compositions having high energy and bulk density are provided in accordance with this invention by incorporating into the composition a ferrophosphorus compound. While even minor amounts of the ferrophosphorus compound enhance the bulk density of the composition, an amount between about 3 and about 25% by weight provides the optimum balance of bulk density and economics. For example, when greater amounts than 50% by weight of the ferrophosphorus compound are provided, the bulk density is proportionally increased, but so is the cost of the resulting explosive.

The ferrophosphorus compound may be added to any conventional blasting agent composition to provide the improvements of the present invention. Particularly preferred compositions, however, are shown in the examples.

In the following examples parts are by Weight unless otherwise indicated. The ferrosilicon in these examples is a commercial electric furnace product consisting by weight of approximately 50% silicon and 50% iron, while the ferrophosphorus compound is a by-product from the manufacture of elemental phosphorus containing approximately 76% iron and 24% phosphorus.

As noted above, other form compounds, particularly ferrosilicon, have been used in some compositions to increase the bulk density. Several such compositions containing ferrosilicon and ferrophosphorus compounds are compared in Examples I-IV to illustrate their relative effectiveness. The energy and strength factors in these examples are computed by conventional procedures from calculated total heat data.

EXAMPLE I To a mixer containing parts of ammonium nitrate granules (less than 20% held on a 35 mesh screen, less than 40% passes through a 100 mesh screen) and 5 parts of ferrophosphorus (less than 12% held on a 100 mesh screen) is added 1 part of calcium stearate. This mixture is mixed for 5 minutes and heated to 125 F. Heating is continued and, after 9 parts of dinitrotoluene is added, mixing is continued for an additional 15 minutes at a temperature of about 140 F. An explosive composition thus is provided having the characteristics shown in column 2 of Table I.

A second composition is provided in the same manner except that ferrosilicon is substituted for the ferrophos- The detonation rate of these compositions is about 11,500 and 11,900 feet per second. The propagation sensitiveness is such that detonation can be propagated from the end of one 2 /2" can to the end of another such can over an air gap of at least /2". The composition cannot be initiated by one No. 8 cap and contains no high explosive ingredients and, therefore classifies as a nitrocarbonitrate.

EXAMPLE 11 Calcium stearate (0.5 part) and paraffin (1.5 parts) are added to a mixer containing 49.0 parts of ammonium nitrate granules (less than 40% held on a 100 mesh screen), 30.0 parts of sodium nitrate granules (at least held on a 20 mesh screen) and 10.0 parts of ferrophosphorus (less than 12% held on a mesh screen). This mixture is heated and mixed further for 3 minutes at which time the temperature of the mix is F. Heating is continued and 9.0 parts of dinitrotoluene are added to the mix. After mixing for another 15 minutes while heating is continued to a temperature of about F., this mix is discharged to provide a composition having the characteristics shown in column 2 of Table Ii.

A second composition is provided in the same manner except that ferrosilicon is substituted for the ferrophosphorus, to provide a composition having the characteristics shown in column 1 of Table II.

. The detonation rate of these compositions is about 16,500 to 16,800 feet per second. The propagation sensitiveness is such that detonation can be propagated from the end of one 5 /2" can to the end of another such can over an air gap of at least 4". This composition is a nitrocarbo-nitrate composition.

EXAMPLE III The compositions of Example I are field tested under similar conditions and there is no strength difference in fact in the rock breakage and burden movement. Similarly there is no strength difi'erence detected in laboratory testing of the compositions of example II. This is wholly unexpected in view of the calculated, strength differences between the compositions containing ferrosilicon and those containing ferrophosphorus.

EXAMILE IV Fine ammonium nitrate (65.1 parts-at least 60% passes through a 100 mesh screen) plus 20 parts of coarser ammonium nitrate (at least 95% held on a 65 mesh screen) are added to a suitable mixer and heated to 175 F. To this is added 0.9 part resin, and the ammonium nitrate is coated by mixing 5 minutes. Then 5 parts of ferrophosphorus, 1 part guhr and 8 parts dinitrotoluene are added and mixed an additional 5 minutes. The mix is discharged between 160 and 180 F. and packed in suitable containers for shipment. The composition thus produced has the characteristics shown in Table III.

Table III Oxygen balance "percent" +1.2 Pressed density g./cc 1.21 Energy, Q heat of explosion, kcal./ kg 900 Strength factor based on Q 10.0

This composition has a rate of detonation of 12,700 feet per second in 3 diameter, and the propagation sensitiveness is such that detonation can be propagated from the end of one cartridge to the end of the next cartridge over an air gap of at least 1 inch. The pressed composition cannot be initiated with one No. 8 cap and contains no high explosive ingredients and, therefore, classifies as a nitro-carbo-nitrate composition.

In addition to the foregoing type of composition wherein a nitrobody is present and the composition is poured hot into containers, ferrophosphorus can be used advantageously in the cold-mixed ammonium nitrate-based compositions.

EXAMPLE V In the preparation of the compositions set forth in Table IV, the order of incorporation of the ingredients in a conventional mixer and the temperature at which the mixing is performed are of no consequence. The ferrophosphorus serves as a fuel which adds considerably to the density of the final composition. In each case, the ammonium nitrate was of such particle size that less than 40% passes through a 100 mesh screen and less than is held on a 35 mesh screen, the sodium nitrate of such particle size that at least 85% is held on a 28 mesh screen, and the ferrophosphorus of a size such that less than 12% is held on a 100 mesh screen. The oil used is of fuel oil grade and the anti-caking agent attapulgus clay.

Composition A has an oxygen balance of -2.2 and detonates with 7 No. 8 blasing caps in a 2-inch diameter.

Composition B has a poured density of 1.10 grams per cubic centimeter and is detonatable in 2-inch diameter with a 9-gram RDX booster.

Composition C has a poured density of 1.09 grams per cubic centimeter and is also detonatable in 2-inch diameter with a 9-gram RDX booster.

The most preferred ferrophosphorus compound contains about 76% iron and about 24% phosphorus, since compounds containing substantially more or less than these amounts are more expensive. Ferrophosphorus compounds containing at least about 10% by weight of phosphorus, however, provide the desired density improvements. The most convenient source of these compounds is as a by-product from the manufacture of elemental phosphorus.

The ferrophosphorus compound can be added to the blasting agent composition at any time during its formulation and mixed in any conventional manner. Generally, it is preferred to admix the dry ingredients first, then add any liquid components to insure level coating of the dry components.

The compositions of the present invention are those known as blasting agents, i.e., do not contain an organic explosive as a sensitizer and are not initiated by one No. 8 blasting cap. The basic component in such compositions is ammonium nitrate.

The screen size of ammonium nitrate granules when treated in accordance with this invention must be controlled so, that from about 30 to 60% passes through a 100 mesh screen, the remainder being sufficiently fine that about 60 to passes through a 65 mesh screen. The particle, size of the other dry ingredients is not critical although when sodium nitrate is added, it is preferred, in general, that the particles be coarser than the ammonium nitrate. The ferrophosphorus particles are preferably finer than the ammonium nitrate granules for optimum results.

Many advantages are provided in accordance with this invention. The ferrophosphorus compound is considerably cheaper than the ferrosilicon; is an alloy, is chemically inert and therefore not subject to rust, and performs equally as well as ferrosilicon in increasing the bulk density of the blasting agent into which it is incorporated while providing the same strength characteristics. Many other advantages will be apparent to those skilled in the art.

I claim:

1. A blasting agent consisting of ingredients which per se are non-explosive, said blasting agent consisting essentially of at least about 50% by weight of ammonium nitrate and about from 3 to 50% by weight of ferrophosphorus.

2. A blasting agent of claim 1 wherein the ferrophosphorus is present in an amount between about 3 and 25% based on the weight of said blasting agent, said ferrophosphorus consisting essentially of iron and on the order of 10 to 24% by weight of phosphorus based on the weight of said ferrophosphorus.

3. A blasting agent of claim 2 wherein the ammonium nitrate is present in the form of granules of a size such that from about 30 to 60% pass through a -mesh screen, the remainder being sufficiently fine that about 6 0 to 90% pass through a 65-mesh screen.

References Cited in the file of this patent UNITED STATES PATENTS 674,159 Blomen May 14, 1901 1,244,940 Arthur Oct. 30, 1917 2,132,996 Palmieri Oct. 11, 1938 2,186,667 Churchill Jan. 9, 1940 2,478,918 Hale et al Aug. 16, 1949 2,768,073 Davidson Oct. 23, 1956 

1. A BLASTING AGENT CONSISTING OF INGREDIENTS WHICH PER SE ARE NON-EXPLOSIVE, SAID BLASTING AGENT CONSSTING ESSENTIALLY OF AT LEAST ABOUT 50% BY WEIGHT OF AMMONIUM NITRATE AND ABOUT FROM 3 TO 50% BY WEIGHT OF FERROPHOSPHORUS. 